1) Field of the Invention
The invention relates to a method for monitoring contaminants in paper pulps and, more particularly, it relates to a method and an apparatus for measuring hydrophobic contaminants in paper pulp suspensions.
2) Description of the Prior Art
The presence of contaminants in paper pulp suspension made from recovery fibers is one of the most important problems in paper mills. Therefore, contaminants control and removal is one of the biggest challenges in the use of recovery fibers. Despite the fact that many methods have been developed for the measurement of contaminants, as evidence by: [M. R. Doshi et al., <<Comparison of Macrostickies Measurement Methods >>, Progress in Paper Recycling, 12(3), 34 (2003); M. R. Doshi et al., <<Comparison of Microstickies Measurement Methods, Part I: Sample Preparation and Measurement Methods >>, Progress in Paper Recycling, 12(4), 35 (2003); M. R. Doshi et al., <<Comparison of Microstickies Measurement Methods, Part II: Results and Discussion >>, Progress in Paper Recycling, 12(4), 35 (2003); J. Kortmeyer et al., <<Identification and quantification of process contaminants from paper mills using old corrugated containers >>, 7e Forum de recherche sur le recyclage, 125 (2004); C. Castro, G. M. Dorris, <<Measuring Microstickies Deposition by Monitoring Pressure Drop Through a Collector >>, Progress in Paper Recycling, 13(3), 23 (2004)], there is still several needs. For instance, all the above methods need specific equipment, extended manipulation and time, thereby preventing their application to large industrial scale. These methods are limited to laboratory level. In addition, the results obtained from these different methods do not always correlate together [M. R. Doshi et al., <<Comparison of Macrostickies Measurement Methods >>, Progress in Paper Recycling, 12(3), 34 (2003); M. R. Doshi et al., <<Comparison of Microstickies Measurement Methods, Part II: Results and Discussion >>, Progress in Paper Recycling, 12(4), 35 (2003)].
U.S. Pat. No. 5,486,904 describes a method for determining the number and the size of resin particles in a pulp suspension. The measurement involves making a pulp suspension; separating resin particles from the pulp suspension by filtration; marking the resin particles with a fluorescent dyestuff and, after singling the resin particles, stimulating light emission; detecting the light signals of the individual resin particles; and evaluating the detection signals to count and determine the size of the resin particles. However, the technique proposed can be difficulty adapted for on-line measurement since the resin particles have to be separated from the pulp suspension.
Similarly, U.S. Pat. No. 5,940,177 describes a method and an apparatus to determine the size distribution of at least two different species in a pulp sample. However, the technique proposed requires separating the contaminant-free particles from the particles including contaminants. Therefore, it is not well suited for on-line measurement.
No fast and easy-to-use instrument for contaminants measurement directly in a paper pulp suspension is available, and only few mills have the time, the equipment and the technical skill to use the laboratory methods described in the literature.